In order to accurately analyze the composition of a sample that consists of mixed refrigerant gases, volatile organic compounds (VOC), hydrocarbon mixtures, or other such substances that exist in gaseous or liquid form at room temperature, samples are taken at the sample collection site, transported to a laboratory, then placed into an analyzer that analyzes the sample.
It is a well known fact that a reliable analysis is obtained by continually injecting the liquid or gaseous sample into the analyzer at a constant pressure.
However, if the sample gas has a high vapor pressure like a hydrocarbon mixture so that even at the same pressure it is a mixture of liquid and gas, the sample being injected into the analyzer will be in an unstable state, making the results of the sample analysis unreliable.
Traditionally, in order to maintain such aforementioned samples in a liquid state to be transported to the laboratory and analyzed, piston type constant pressure cylinders that use o-rings (Piston Type Constant Pressure Cylinder, 600), such as those depicted in the conceptual diagrams of FIG. 11 and FIG. 12, were utilized.
In other words, the aforementioned piston type constant pressure cylinder (600) is comprised of, as shown in FIG. 11, a sample chamber (601) that collects the sample; an inert gas chamber (602) into which an inert gas is injected so as to raise the pressure in the sample chamber (601) in accordance with the amount injected without affecting the sample; an o-ring piston (603) that forms a movable partition located in between the aforementioned sample chamber (601) and the inert gas chamber (602); opening/closing valves (604),(604′) on the aforementioned sample chamber (601) and inert gas chamber (602); and connecting parts (605),(605′) that connect the aforementioned sample chamber (601) and inert gas chamber (602) to the gas analysis system.
This aforementioned traditional piston type constant pressure cylinder (600) has a plurality of o-rings interposed on the edge of the end plate of the o-ring piston, and the o-ring piston (603) is coupled to allow for back and forth movement.
Furthermore one side of the cylinder divided by the aforementioned o-ring piston (603) forms the sample chamber (601), while the other side forms the inert gas chamber (602).
The aforementioned piston-type constant pressure cylinder (600) adjusts the pressure within the sample chamber (601) to the appropriate pressure by first closing the opening/closing valve (604) after filling the sample chamber (601) with the sample, then gradually increasing the amount of inert gas injected into the inert gas chamber (602).
In other words, when the sample within the aforementioned sample chamber (601) is in a liquid state, the injection of inert gas is stopped and the opening/closing valve (604) of the inert gas chamber (602) is closed.
At this point, as shown in FIG. 12, as the internal pressure of the inert gas chamber (602) goes up in response to the increase in the amount of inert gas injected, the o-ring piston (603) cannot overcome this pressure and is pushed towards the sample chamber (601) side, making the pressure inside the sample chamber (601) go up, and when the pressure within the sample chamber (601) is adjusted to the predetermined pressure, the opening/closing valve (604) of the inert gas chamber (602) is closed and the aforementioned piston-type constant pressure gas transport apparatus (600) is removed and transported to the laboratory after which, as shown in FIG. 13, it is installed onto the analyzer so as to analyze the composition of the sample.
However, while the aforementioned traditional piston-type constant pressure cylinder contributes somewhat to adjustments of the pressure within the sample chamber (601) to the appropriate pressure, as there are a plurality of o-rings interposed on the edge of the end plate of the o-ring piston and the piston is formed to allow for back and forth movement, leaks of trace amounts of gas form at the o-rings on the edge of the end plate of the piston, making it difficult to maintain constant pressure within the sample chamber or altering the composition of the sample, so as a result the sample within the sample chamber contains both liquid and gas, making the sample composition analysis unreliable.
In particular, when the sample contains trace amounts of a substance, the state of the sample being injected into the analyzer undergoes minute changes, making the composition analysis even more unreliable.